1. Field of the Invention
This invention relates to a lubricating oil additive and lubricating oils incorporating a minor proportion of said additive to depress the pour point of said oil.
The additive is the copolymer of 1-olefins, said 1-olefin being a mixture comprising from about 25 to 75 mole percent of a straight chain C.sub.20-24 higher olefin and from about 25 to 75 mole percent of a C.sub.10-14 lower olefin, and maleic anhydride, said 1-olefins and said anhydride being present in about equimolar amounts. The additive can be usefully esterified with alcohols having one to eight carbons, e.g., 2-ethyl hexanol.
2. Prior Art
A wide variety of compositions comprising polymeric materials derived from the addition reaction of alpha-olefins and dicarboxylic alkenes have been described in the literature as dispersants for fuels and lubricants, and as viscosity index improvers for lubricants.
U.S. Pat. No. 2,615,845 teaches that the copolymer of maleic anhydride and a straight chain alpha-olefin having up to 24 carbon atoms (see claim 2), which is subsequently esterified with long, straight chain, saturated alcohols in order to make it suitably oil-soluble, can be usefully added to a mineral lubricating oil for pour point depression.
U.S. Pat. No. 2,542,542 discloses the general preparation of copolymers of ethylene-1,2 dicarboxylic acids, and their derivatives and long chain olefins containing from 8 to 24 carbon atoms and shows only copolymers derived from 1-octadecene to be useful as lubricating oil pour point depressants.
U.S. Pat. No. 2,655,479 points out that a factor of particularly great effect on the pour depressant activity of acrylic ester polymers is the length of the alkyl side chains (apparently a function of the oil solubilizing effect of the alkyl side chain). This factor, however, is further limited by the consideration that the "polymers of single esters are rarely pour point depressants".
U.S. Pat. No. 2,977,334 teaches a copolymer of ethylene with maleic anhydride, wherein the maleic anhydride units are subsequently partially esterified or aminated. The patentee teaches various alcohols, including 2-ethylhexyl (column 4, line 32) for this purpose.